The invention relates to a process for applying a layered structure on a convex surface of a lens. It may be implemented with an ophthalmic lens, in particular.
It is often useful to fit a lens with a film on a surface of that lens, for obtaining a resulting lens which has a desired property. For example, the film may be a polarizing film, a contrast-enhancing film, a photochromic film, etc. Because the surface of the lens is curved, the film cannot be directly applied on the lens when it has a planar shape. Indeed delaminations, cracks and/or wrinkles would then occur, due to the difference in curvature between the film and the lens surface. Therefore, it is necessary to preform the film, so as to provide it with an initial curvature before application on the lens surface.
It is also known to provide a layered structure with a curved shape, so that the layered structure has a first surface which is concave and a second surface which is convex. Then, the first surface of the layered structure is brought into contact with the lens surface at an initial contact point, preferably in a middle part of the lens surface. Starting from the initial contact point, the first surface of the layered structure is pushed against the lens surface via pressure applied on the second surface of the layered structure. The contact between the first surface of the layered structure and the lens surface continuously expands radially as pressure is increased. In known implementations of such process, a peripheral edge of the layered structure is hold during the application on the lens, and the structure is pushed against the lens with a resilient pad.
But despite the layered structure is initially provided with a curved shape, the lens fitted with the layered structure exhibits wrinkles in the structure near in a peripheral part of the lens, or cracks in the layered structure in the middle part of the lens. Such defects occur especially when the curvature radius of the lens surface is small, typically less than 75 mm (millimeters).